How to make my water look Murky?
This method will be pretty hard for your hardware, but it's the only reasonable way (I can think of) to make it look good from any angle.

Any other method I've tried like using gradient to change Roughness, Transmission, mixing with other shader is looking similar from the side but they will not work looking from above. 

It's really simple setup. 



First of all you will need to use Separate XYZ to be able to create gradual transition between dirt and clear water. 

Next you can use this separation to create water color change (not necessary) and use Principled or Glass shader for water itself.

Lastly add Volume Scatter and Absorption to make "dirt" inside your water. Multiply node will help with Density - higher value = denser dirt.

Don't forget to crank up Light Paths > Volume to something higher than 0. I've used 2 in this example.